Thermal expansion of the Sn₂P₂(Se_0.28S_0.72)₆ solid solutions

Abstract

In the present work, we have experimentally studied and analysed the dilatometric properties of Sn₂P₂(Se_0.28S_0.72)₆ crystals during ferroelectric phase transition. A complete matrix of thermal expansion tensors as well as the characteristic surface of the thermal expansion tensor has been obtained. The critical exponent for the volume thermal expansion coefficient in Sn₂P₂(Se_0.28S_0.72)₆ crystals has been determined to be equal to 0.50 ± 0.06, which is peculiar to tricritical behaviour. Non-agreement in the values of the critical exponents evaluated from the temperature dependencies of relative elongation (0.17 ± 0.01) and volume thermal expansion coefficient (0.50 ± 0.06) is shown to be due to the possible temperature rotation of the spontaneous polarisation vector.

Keywords:

• ferroelectrics
• phase diagram
• thermal expansion
• Liftshitz point

Acknowledgements

The authors thank Professor Yu.M. Vysochanskii and Professor A.A. Grabar for useful discussions and samples during the STCU Project No. 3623. The Scientific and Technology Centre in Ukraine is thanked for financial support of the present study.